Volume control circuits



p 10, 1940- E. w. 'HEROLD 2,214,613

VOLUME CONTROL CIRCUITS 7 Filed March 23, 1939 DETECTOR v 6 3 2 f 70 I F j 4 T 4.5

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r0 SIGNALGR/DS 7 OF PRIOR 70555 liq-2 DETECTOR A. E AMPL NE TWORK AVC AF. MEL Q INVENTOR. EDWARD m HEROLD ATTORNEY.

Patented Sept. 10, 1940 VOLUME CONTROL CIRCUITS by Edward W. Herold, Verona, N. J assignor to Radio Corporation of America, a corporation of Delaware Application March 23, 1939, Serial N0. 263,602

8 Claims.

My present invention relates tovolume control circuits for audio amplifiers, and more particularly to simplified gain control connections between a diode detector and a subsequent audio One of the important objects of my invention is toprovide, in a radio receiver, a signal detector of the diode type which supplies its audio voltage output to a succeeding audio amplifier 10 through'a potentiometer; the potentiometer being so constructed that the audio amplifier signal grid has its potentialvaried in accordance with the direct current voltage output of the detector, and the audio signal grid being connected to the diode anode solely through the potentiometer resistor.

Another important object of this invention may be stated to reside in the provision of a diode detector which has in its output circuit a resistorcondenser network functioning simultaneously as 20 the manual volume control device for a succeeding audio amplifier and as the filter for an automatic volume control connection to one or more preceding signal amplifiers.

Still other objects of my invention are to im- 25 prove generally the simplicity, compactness and efiiciency of audio coupling connections between a diode' detector and a succeeding audio amplifier, .and more especially to provide adjustable audio connections to diodedetectors in a manner 30 which is not only reliable and efficient in operation, but is economically manufactured and assembledin radio receivers. I

v The novel features which I believe to be characteristic of my invention are set forth in par- 35 ticularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have in- 40 dicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing:

Fig. 1 shows an embodiment of the present 45 invention;

Fig; 2 illustrates a modification; and

'Fig. 3 illustrates a further modification.

Referring now to the accompanying drawing, wherein like reference characters in the different 5 figures designate similar circuit elements, there is tector is of the diode type, and the diode I has its anode 2 connected to its grounded cathode through a path which includes in series the resonant input circuit 3 and the load impedance 4. The impedance 4 is shunted by a carrier by-pass {5: condenser 5, and the input circuit 3 is tuned to the operating carrier frequency. If the receiver is of the superheterodyne type, then circuit 3 is tuned to the operating intermediate frequency (I. F.) and it will be understood that numeral 6 1 0 denotes the intermediate frequency output circuit of the final intermediate frequency amplifier. It

is not believed necessary to explain in detail the construction of the various signal amplifier networks which may precede circuit 6, since those skilled in the art are very well acquainted with such networks.

The audio and direct current voltage components developed across impedance 4 are utilized as shown in Fig. 1. The direct current voltage component is employed automatically to regulate the gain of one or more of the preceding signal carrier amplifiers, and such automatic volume control circuit is designated by the letters AVG. The gain control connection 7 is made to the anode end of resistive impedance 4 through a resistor 8, the resistor being connected to ground through a condenser 9. This resistor-condenser network provides the usual filter for removing pulsation voltage components from the gain control voltage.

The audio voltage component of the rectifier output voltage is utilized for subsequent audio frequency amplification. This is accomplished by providing the audio frequency amplifier II], and the signal grid of the latter is connected to the anode end of impedance 4 through the. potentiometer comprising resistor II and adjustable tap l2. One end of resistor II is connected directly to the anode end of resistor 4, while its opposite end is connected to ground through the capacitor I3. The cathode of amplifier I0 is connected to ground through the usual self-biasing network l4, and it is to be understood that the audio voltage output of amplifier l 0 will be transmitted through one or more subsequent amplifiers, and finally reproduced by any desired type of audio reproducer.

It will be observed that the signal grid of amplifier HI normally, that is in the absence of incoming carrier signals, has a negative bias applied to it through a path which includes tap l2, resistor ll, load impedance 4, ground and the biasing resistor of the audio amplifier. As soon as carrier energy is-received, and the amplitude of the carrier increases, then the signal grid of amplifier I0 has its negative bias increased.

.There is thus provided automatic gain regulation of both the pre-detector stages and the subsequent audio amplifier. Adjustment of tap 12 with respect to resistor I 1 provides adjustment of the magnitude of the audio voltage impressed on the audio amplifier; the potentiometer Ill2, therefore, acts as a manual volume control device to regulate the loudness of audio reproduction.

The direct current voltage from the diode load impedance 4 is impressed on the signal grid of amplifier l0 directly through the potentiometer resistor l I, while the audio voltage component is attenuated by adjustment of the potentiometer tap [2. This is true because the lower end of the potentiometer resistor is effectively at alternating current ground potential through the condenser [3. This circuit is of advantage in that, under average conditions, a lower direct current resistance is obtained in the grid circuit of amplifier l0 than with other well-known arrangements which accomplish the same result. At the same time, the efiects of any grid current flow in the grid circuit of amplifier ill on the operation of. the predetector tubes are highly minimized.

In the arrangement shown in Fig. 2 the functions of the elements in Fig. 1, and which elements are included in the audio and direct current connections to the detector, are provided with a minimum of parts. In this case the potentiometer resistor H and the condenser l3 function simultaneously as the manual volume control device and the automatic volume control filter network. It will be observed that in this arrangement the automatic volume control connection I is made to the junction of resistor H and condenser l3, so that the lead derives the direct current voltage from the load impedance through the potentiometer resistor II. The resistor l! and condenser l3 are chosen in magnitude so that they provide a proper suppression of pulsation voltages with the result that the control voltage transmitted over lead 1 is properly filtered. At high volume control settings of tap 62 the direct current resistance of the grid circuit of amplifier It), which is common to the controlled pre-detector tubes, is considerably reduced so that, in this condition, any undesirable grid current fiow in tube iii has but little effect on the operation of the pre-detector tubes.

It is frequently desirable to add a bass-compensating network to the volume control circuit of Fig. 2. Fig. 3 shows a circuit incorporating such a network connected to a fixed tap on volume control ii. The network consists of a resistance 15 and capacitance i i. The AVC voltage for the pre-detector stages is taken from lead 1 which is connected to the junction of elements it and i5. By this means, the time constant of the AVG network is not too large, as it might be if it were connected to the junction of elements H and is of Fig. 3. The circuit of Fig. 3 has an advantage over that of Fig. 2 in that the audio volume at minimum setting of the slider I2 is considerably less, and, in fact, may be made negligibly small.

It should be understood that my invention is not limited to the specific embodiments shown in the figures. For example, it is sometimes desirable to add additional filtering of the radio frequency, or intermediate frequency, alternating voltages to that already provided by the capacitance 5. Such additional filtering between the diode detector and the audio amplifier is well known in the art, and it is, unnecessary to elaborate on such a modification here. It is also understood that the potentiometer ll may be modified to include additional taps for automatic bass compensation.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no'means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In a signal receiver, a diode detector network including a load impedance across which are developed audio and direct current voltages, an audio amplifier having a signal input grid, a path comprising a resistor and condenser in shunt to said impedance, an adjustable connection between the grid and said resistor for regulating the magnitude of the audio voltage impressed on the grid, and an automatic volume control circuit connected to the junction of said resistor and condenser. I

2. In a signal receiver, a diode detector network including a load impedance across which are developed audio and direct current voltages, an audio amplifier having a signal input grid, a path comprising a resistor and condenser in shunt to said impedance, an adjustable connection between the grid and said resistor for regulating the magnitude of the audio voltage impressed on the grid, said resistor and condenser being chosen to function as a filter network for the direct voltage, and an automatic volume control circuit connected to the junction of said resistor and condenser.

3. In a radio receiver of the type comprising a diode rectifier having an input circuit adapted to be coupled to a signal amplification network, an audio amplifier provided with input and output electrodes, said rectifier including a loadimpedance for developing audio and direct current voltages from rectified signal currents fiowa ing through the impedance, an automatic gain control connection to a point on said impedance which becomes increasingly negative with signal carrier amplitude increase, said connection including a filter resistor, a second gain control connection from said amplifier input electrode, said second connection including an adjustable tap slidable along said resistor to vary the magnitude of audio voltage impressed on the input electrode.

4. In a radio receiver of the type comprising a diode rectifier having an input circuit adapted to be coupled to a signal amplification network, an audio amplifier provided with input and output electrodes, said rectifier including a load impedance for developing audio and direct current voltages from rectified signal currentsfiowing through the impedance, an automatic gain control connection to a point on said impedance which becomes increasingly negative with signal carrier amplitude increase, said connection including a resistor, a second gain controlconnection from said amplifier input electrode, said second connection including an adjustable tap slidable along said resistor to vary the magni-,

tude of audio voltage impressed on the input electrode, and a condenser in series with said resistor across said impedance, the resistor and condenserproviding a filter for removing pulsaid automatic control connection.

5. In combination with a signal carrier receiving system including a detector and carrier gain control network, said detector having a load impedance across which is generated direct and audio voltages, an audio volume control resistor consisting of a potentiometer with an adjustable tap, a first connection from one end of said volume control resistor to a point on the detector load impedance, said first connection being adapted for the transmission of the direct current and at least part of the demodulation products which result from rectification by said detector of a received signal, a second connection from the other end of said volume control resistor through a capacitance to a second point on the detector load impedance, an amplifier system with an electron discharge tube having two input electrodes one of which is connected to the variable tap on the aforementioned volume control resistor and the other of which is connected to the said second point on the detector load impedance, and a connection from said other end of the volume control resistor to the aforementioned carrier gain control network.

6. In combination with a signal carrier receiving system including a detector and carrier gain control network, said detector having a load impedance across which is generated direct and audio voltages, an audio volume control resistor consisting of a potentiometer with an adjustable tap, a first connection from one end of said volume control resistor to a-point on the detector load impedance, said first connection being adapted for the transmisison of the direct current and at least part of the demodulation prod ucts which result from rectification by said detector of a received signal, a second connection from the other end of said volume control resistor through a capacitance to a second point on the detector load impedance, an amplifier system with an electron discharge tube having two input electrodes one of which is connected to the variable tap on the aforementioned volume control resistor and the other of which'is connected to the said second point on the detector load impedance, and a connection from an intermediate point on said volume control resistor to a frequency discriminating network including a second capacitance, one end of which is connected to said other end of the volume control resistor and the other end of which is connected to the aforementioned carrier gain control network.

7. In combination with a signal carrier receiving system including adetector and carrier gain control network, said detector having a load impedance across which is generated direct and audio voltages, an audio volume control resistor consisting of a potentiometer with an adjustable tap, a first connection from one end of said volume control resistor to a point on the detector load impedance, said first connection being adapted for the transmission of the direct current and at least part of the demodulation products which result from rectification by said detector of a received signal, a second connection from the other end of said volume control resistor through a capacitance to a second point on the detector load impedance, an amplifier system with an electron discharge tube having two input electrodes one of which is connected to the variable tap on the aforementioned volume control resistor and the other of which is connected to the said second point on the detector load impedance, and a connection from an intermediate point on said volume control resistor to one end of a resistance whose other end is connected to both the aforementioned carrier gain control network and to one side of a second capacitance, said second capacitance having its other side connected to said second point on the detector load impedance.

8. In combination with a signal carrier receiving system including a detector and carrier gain control network, said detector having a load impedance across which is generated direct and audio voltages, an audio volume control resistor consisting of a potentiometer with an adjustable tap, a first connection from one end of said volume control resistor to a point on the detector load impedance, said first connection, being adapted for the transmission of the direct current and at least part of the demodulation products which result from rectification by said detector of a received signal, a second connection from the other end of said volume control resistor through a capacitance to a second point on the detector load impedance, an amplifier system with an electron discharge tube having two input electrodes one of which is connected to the variable tap on the aforementioned volume control resistor and the other of which is connected to the said second point on the detector load impedance, and connections from at least one intermediate point on said volume control resistor to a frequency discriminating network, which is also adapted for connection to the aforesaid carrier gain control network.

EDWARD W. HEROLD. 

